Al-Qaeda's front group in Iraq said Wednesday that a wave of attacks that killed 113 days earlier marked the launch of a new offensive, as officials said seven people died in new unrest.

The spate of violence nationwide on Monday, which also wounded more than 250 people, was the worst to hit Iraq in more than two and a half years and shattered a relative calm that had held in the lead-up to the holy Muslim fasting month of Ramadan.

On Wednesday, the Islamic State of Iraq claimed the attacks in a statement posted on jihadist forum Honein.

"As part of the new military campaign aimed at recovering territory given up by the Islamic State of Iraq (ISI), the war ministry has sent its sons and the mujahedeen on a sacred offensive during the month of Ramadan," the group said.

"The operation by the jihadists has stunned the enemy and made him lose his head. It has demonstrated the failings of the security and intelligence services," it continued.

Last weekend, the group said it would look to retake territory, and appealed for Sunni tribes to provide support and send fighters, in an Internet audio message purportedly left by its leader Abu Bakr al-Baghdadi.

The message posted on various jihadist forums said the ISI would begin targeting judges and prosecutors, and try to help its prisoners break out of Iraqi jails.

"We are starting a new stage," said the voice on the audio message, purportedly that of Baghdadi.

Al-Qaeda in Iraq is regarded by Iraqi officials as significantly weaker than at the peak of its strength in 2006 and 2007, but it is still capable of spectacular mass-casualty attacks across the country.

Late Tuesday, meanwhile, a car bomb in the town of Ad-Dawr, in Salaheddin province north of Baghdad, killed the wife and four children of a police captain, police and medics said.

Also on Tuesday evening, another blast, this time a roadside bomb in south Baghdad, killed at least two people and wounded three others, security and medical officials said.

The attacks came a day after Monday's spate of bombings and shootings, which drew widespread international condemnation.

The wave of violence consisted of at least 29 separate attacks in 19 cities, with most of the unrest concentrated in Baghdad and areas north of the capital.

In the deadliest incidents -- a string of roadside bombs and a car bomb followed by a suicide attack targeting emergency responders in the town of Taji, just north of Baghdad -- at least 42 people were killed and 40 wounded, medical officials said.

US State Department spokeswoman Victoria Nuland told reporters Washington strongly condemned the attacks.

"The targeting of innocents is always cowardly," she said. "It's particularly reprehensible during this holy month of Ramadan."

The violence also drew condemnation from the United Nations special envoy to Iraq, the country's parliament speaker, as well as France, Canada and neighbouring Iran.

Monday's toll was the highest since December 8, 2009, when 127 people were killed.